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what rear end would be better for a KA engine?

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why did the roadster have a 3.90 in the 1600 and a 3.7 with the 2000, because of the smaller size 1.6L?


Well doesnt the L16 rev higher than the L20b? so higher rev takes car of lower gearing, Engine not as torqy. L20b definitely has more torque and therefor can take the lower gearing. I imagine this might be true with the R16/R20.

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Massive hp works better with super high gears. Basically the higher the gear ratio, the less torque multiplication you have, the higher theoretical top speed, and the best mileage to the point of diminishing return.


Lower gears are better for climbing, acceleration, and power out of low hp motors. For instance, I'm running 4.11s in the 510 right now. Combined with the L20 and the goofy shift (close ratio) 5 speed, the 510 rips up, but also has an rpm limited redline of 120. That's at 6500 rpm in 5th gear. That means I'm turning 3500 in 5th at 60 mph on the freeway. Not exactly ideal. But I want my acceleration factor, so I deal with it.


The KA probably has enough hp to push 3.7s just fine, however, with the KA trans, you'll be really tall geared. Think pulling 1500 rpm in 5th on the freeway, yet not having enough power to push into the 140 mph range because it's just not enough power.


I ran the stock 3.7 Subi diff rear end in the 510 for a while. It was definitely high geared, and I couldn't even come close to redlining in 5th. It moved the theoretical top speed much higher, but not enough oomph to get there.


I'd go with the 3.9s. Still good economy, but also good power.

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3.7 or 3.9 ?

would it be a negligible difference?

My 510 has the vg six cylinder. It still has the stock 3.90 rear end,first gear is useless its like a compound low in an old pickup.I just picked up a 3.70 lsd I think it will make a difference atleast a little.

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